Often when going to the beach the common complaint is that the ocean is too cold. They appear to be warming up a bit.
The upper layer of Earth's ocean has warmed since 1993, indicating a strong climate change signal, according to a new international study co-authored by oceanographer Josh Willis of NASA's Jet Propulsion Laboratory, Pasadena, Calif. The energy stored is enough to power nearly 500 100-watt light bulbs for each of the roughly 6.7 billion people on the planet.

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"We are seeing the global ocean store more heat than it gives off," said John Lyman, an oceanographer at the National Oceanic and Atmospheric Administration's (NOAA) Joint Institute for Marine and Atmospheric Research, who led the study that analyzed nine different estimates of heat content in the upper ocean from 1993 to 2008.

The team combined the estimates to assess the size and certainty of growing heat storage in the ocean. Their findings will be published in the May 20 edition of the journal Nature. The scientists are from NASA, NOAA, the Met Office Hadley Center in the United Kingdom, the University of Hamburg in Germany and the Meteorological Research Institute in Japan.

"The ocean is the biggest reservoir for heat in the climate system," said Willis. "So as the planet warms, we're finding that 80 to 90 percent of the increased heat ends up in the ocean."

A warming ocean is a direct cause of global sea level rise, since seawater expands and takes up more space as it heats up. The scientists say that this expansion accounts for about one-third to one-half of global sea level rise.

Combining multiple estimates of heat in the upper ocean — from the surface to about 610 meters (2,000 feet) down — the team found a strong multi-year warming trend throughout the world's ocean. According to measurements by an array of autonomous free floating ocean floats called Argo, as well as by earlier devices called expendable bathythermographs, or XBTs, that were dropped from ships to obtain temperature data, ocean heat content has increased over the last 16 years.

The team notes that there are still some uncertainties and some biases.

Most people, when hearing or reading about a warm up of the world ocean, would naturally ask: How much? But to scientists who study phenomena like this, the problem is more complex. While they use ocean temperature readings taken from around the globe to conduct their studies on ocean warming, these scientists are interested in learning about the heat content of the world ocean’s enormous mass of water. Heat content is a measure of the heat energy imparted to a body such as a continent or the ocean. Scientists measure heat content in energy units known as joules.

Beginning in the 1970s, scientists at NOAA’s Geophysical Fluid Dynamics Laboratory in Princeton, New Jersey, started computing the annual cycle of ocean heat content. From the outset, scientists in the climate modeling community showed significant interest in the results of this work as a way to validate their general circulation models of ocean atmosphere interactions.

For further information: http://www.jpl.nasa.gov/news/news.cfm?release=2010-169